Prerequisites

Network policies are implemented by the network plugin, so you must be using a networking solution which supports NetworkPolicy - simply creating the resource without a controller to implement it will have no effect.

Isolated and Non-isolated Pods

By default, pods are non-isolated; they accept traffic from any source.

Pods become isolated by having a NetworkPolicy that selects them. Once there is any NetworkPolicy in a namespace selecting a particular pod, that pod will reject any connections that are not allowed by any NetworkPolicy. (Other pods in the namespace that are not selected by any NetworkPolicy will continue to accept all traffic.)

spec: NetworkPolicyspec has all the information needed to define a particular network policy in the given namespace.

podSelector: Each NetworkPolicy includes a podSelector which selects the grouping of pods to which the policy applies. The example policy selects pods with the label “role=db”. An empty podSelector selects all pods in the namespace.

policyTypes: Each NetworkPolicy includes a policyTypes list which may include either Ingress, Egress, or both. The policyTypes field indicates whether or not the given policy applies to ingress traffic to selected pod, egress traffic from selected pods, or both. If no policyTypes are specified on a NetworkPolicy then by default Ingress will always be set and Egress will be set if the NetworkPolicy has any egress rules.

ingress: Each NetworkPolicy may include a list of whitelist ingress rules. Each rule allows traffic which matches both the from and ports sections. The example policy contains a single rule, which matches traffic on a single port, from one of three sources, the first specified via an ipBlock, the second via a namespaceSelector and the third via a podSelector.

egress: Each NetworkPolicy may include a list of whitelist egress rules. Each rule allows traffic which matches both the to and ports sections. The example policy contains a single rule, which matches traffic on a single port to any destination in 10.0.0.0/24.

So, the example NetworkPolicy:

isolates “role=db” pods in the “default” namespace for both ingress and egress traffic (if they weren’t already isolated)

allows connections to TCP port 6379 of “role=db” pods in the “default” namespace from any pod in the “default” namespace with the label “role=frontend”

allows connections to TCP port 6379 of “role=db” pods in the “default” namespace from any pod in a namespace with the label “project=myproject”

allows connections to TCP port 6379 of “role=db” pods in the “default” namespace from IP addresses that are in CIDR 172.17.0.0/16 and not in 172.17.1.0/24

allows connections from any pod in the “default” namespace with the label “role=db” to CIDR 10.0.0.0/24 on TCP port 5978

Default policies

By default, if no policies exist in a namespace, then all ingress and egress traffic is allowed to and from pods in that namespace. The following examples let you change the default behavior
in that namespace.

Default deny all ingress traffic

You can create a “default” isolation policy for a namespace by creating a NetworkPolicy that selects all pods but does not allow any ingress traffic to those pods.

This ensures that even pods that aren’t selected by any other NetworkPolicy will still be isolated. This policy does not change the default egress isolation behavior.

Default allow all ingress traffic

If you want to allow all traffic to all pods in a namespace (even if policies are added that cause some pods to be treated as “isolated”), you can create a policy that explicitly allows all traffic in that namespace.

This ensures that even pods that aren’t selected by any other NetworkPolicy will not be allowed egress traffic. This policy does not
change the default ingress isolation behavior.

Default allow all egress traffic

If you want to allow all traffic from all pods in a namespace (even if policies are added that cause some pods to be treated as “isolated”), you can create a policy that explicitly allows all egress traffic in that namespace.